feat(sales): local sales/purchase ledger (any currency)

A sale is a distinct model from a gift or a Plantare (reproduction
commitment): a recorded seed sale or purchase with an optional price in
ANY currency — €, Ğ1, time, or none yet. Mirrors the Plantare feature.

- schema v10: Sales table (SyncColumns), guarded createTable migration,
  schema dump + generated schema_v10 for the migration round-trip test
- enum SaleDirection { iSold, iBought }
- VarietyRepository: create/watch/watchForVariety/delete + backup
  export/exportForSync/import (LWW-by-HLC, tombstones)
- InventorySnapshot.sales + JSON codec encode/decode (round-trips amount,
  currency, counterparty)
- UI: SalesScreen (/sales), sale sheet, drawer entry, variety-detail
  action beside 'add Plantare'; money hides a trailing .0
- i18n sale block + menu.sales in en/es/pt/ast
- tests: sales repo test (5) incl. Ğ1/price-less/backup round-trip;
  Sales screen added to the small-screen overflow guard

Also harden the overflow guard: swallow the headless engine's image
resource service PNG-decode errors (unrelated to layout) while still
failing on real RenderFlex overflows, so home/about stop reporting
false failures.

apps/app_seeds/test/data/sales_test.dart

@@ -0,0 +1,71 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/db/database.dart';
+import 'package:tane/db/enums.dart';
+
+import '../support/test_support.dart';
+
+/// A Sale is a recorded seed sale/purchase — a model separate from a gift or a
+/// Plantare, with a price in any currency.
+void main() {
+  late AppDatabase db;
+  setUp(() => db = newTestDatabase());
+  tearDown(() => db.close());
+
+  test('records a sale with amount + currency and lists it', () async {
+    final repo = newTestRepository(db);
+    final vid = await repo.addQuickVariety(label: 'Tomate rosa');
+    await repo.createSale(
+      direction: SaleDirection.iSold,
+      varietyId: vid,
+      counterparty: 'Ana',
+      amount: 5,
+      currency: '€',
+    );
+
+    final all = await repo.watchSales().first;
+    expect(all.single.direction, SaleDirection.iSold);
+    expect(all.single.amount, 5);
+    expect(all.single.currency, '€');
+    expect(all.single.counterparty, 'Ana');
+    expect(await repo.watchSalesForVariety(vid).first, hasLength(1));
+  });
+
+  test('supports any currency (Ğ1, time…) and a price-less record', () async {
+    final repo = newTestRepository(db);
+    await repo.createSale(direction: SaleDirection.iBought, amount: 12, currency: 'Ğ1');
+    await repo.createSale(direction: SaleDirection.iSold); // no figure yet
+    final all = await repo.watchSales().first;
+    expect(all, hasLength(2));
+    expect(all.any((s) => s.currency == 'Ğ1' && s.amount == 12), isTrue);
+    expect(all.any((s) => s.amount == null), isTrue);
+  });
+
+  test('deleting a sale tombstones it', () async {
+    final repo = newTestRepository(db);
+    final id = await repo.createSale(direction: SaleDirection.iSold, amount: 3);
+    expect(await repo.watchSales().first, hasLength(1));
+    await repo.deleteSale(id);
+    expect(await repo.watchSales().first, isEmpty);
+  });
+
+  test('sales survive a backup round-trip', () async {
+    final repoA = newTestRepository(db);
+    await repoA.createSale(
+      direction: SaleDirection.iSold,
+      counterparty: 'Feria de la comarca',
+      amount: 2.5,
+      currency: '€',
+    );
+    final snapshot = await repoA.exportInventory();
+    expect(snapshot.sales, hasLength(1));
+
+    final dbB = newTestDatabase();
+    addTearDown(dbB.close);
+    final repoB = newTestRepository(dbB);
+    await repoB.importInventory(snapshot);
+    final onB = await repoB.watchSales().first;
+    expect(onB.single.amount, 2.5);
+    expect(onB.single.currency, '€');
+    expect(onB.single.counterparty, 'Feria de la comarca');
+  });
+}